The present invention relates to an outboard motor having an intake silencing box which constitutes an intake silencer.
Outboard motors without intake silencers and outboard motors with their intake openings directed toward the hulls produce intake noises which are transmitted directly to the manipulators and hence are noisy.
Intake silencers are thus provided in intake passages to reduce intake noises. An outboard motor with such a conventional intake silencer is disclosed in, for example, Japanese Patent Laid-Open Publication No. HEI-8-310487.
The conventional intake silencer is disposed in an intake system of an engine of the outboard motor. The intake silencer takes air in from laterally opposite sides of a throttle body provided in a front and laterally generally middle portion within an engine space of the outboard motor. The total cross-sectional area of the two air inlets of the intake silencer is equal to or greater than the cross-sectional area of an intake passage of the throttle body, securing a sufficient amount of intake, reducing the dimension of one air inlet, and thus increasing space efficiency.
The arrangement disclosed in HEI-8-310487 has an air inlet portion located relatively closely to the front part of the engine. In some cases, however, no space is available for the air inlet portion.
The present invention has been made to solve the above problem and has an object of providing an outboard motor causing no interference between an exhaust passage and an air inlet portion in a portion of the outboard motor other than a portion closer to the front of the engine, regardless of the presence of the exhaust passage at the side of a cylinder head.
It is another object of the present invention to provide an outboard motor with a V-engine in a plan view which can utilize the contour of the V-engine to put an intake silencing box within the opening width dimension of the V shape, securing a sufficient volume of an expansion chamber and a sufficient intake opening of the intake silencing box, preventing increase in the size of the intake silencing box, and increasing noise-reduction efficiency.
It is a particular object of the present invention to provide an outboard motor with an intake silencing box which allows the use of an intake silencing box of a large volume while avoiding increase in the size of the intake silencing box, and allows preferable intake of air into the intake silencing box.
It is another object of the present invention to provide an outboard motor which allows a rational arrangement of an intake silencing box constituting an intake silencer, an alternating-current generator (ACG) and other components.
According to an aspect of the present invention, there is provided an outboard motor having a four-stroke engine, which comprises: a generally vertically extending crankshaft; a cylinder block constituting part of a crankcase housing the crankshaft, the cylinder block having a plurality of generally horizontal cylinders; a cylinder head connected to a rear surface of the cylinder block to form a plurality of combustion chambers; an exhaust passage provided at one side of the cylinder head in communication with the combustion chambers; an intake passage provided at the other side of the cylinder head in communication with the combustion chambers; and an intake silencing box provided above the cylinder block in communication with the combustion chambers via the inlet passage, wherein the intake silencing box has an air induction passage disposed forwardly of the exhaust passage and extending vertically downwardly between the exhaust passage and a skirt portion of a crankshaft space in a suspended fashion, the air induction passage having an air inlet opening downwardly.
Since the air induction passage of the intake silencing box is disposed forwardly of the exhaust passage and extends downwardly between the exhaust passage and the skirt of the crankshaft space in a suspended fashion, interference between an exhaust pipe constituting the exhaust passage and the inlet passage is prevented. It is thus possible to provide an intake silencing box of a large volume while avoiding increase in the lateral size of the outboard motor and reducing the outer size of the outboard motor.
In order to secure a sufficient steering angle especially when two outboard motors are fixed in parallel to the stern, it is required to reduce the lateral dimension of the outboard motors, reducing space in the front of the engines. This invention provides an outboard motor of a small width dimension fulfilling the requirement, requiring less space in the front.
Since the air induction passage of the intake silencing box is extended downward between the exhaust passage and the skirt of the crankshaft space with the inlet opened, the flow of air into the intake silencing box first moves upward from the inlet and then enters the silencing chamber. This prevents water from entering the intake silencing chamber, regardless of the location of an air inlet of an engine cover.
Preferably, the engine comprises a V-engine with the vertically adjacent cylinders forming a rearward-opening V shape as viewed from the top. The cylinders are thus arranged to the shape of angled cylinders of the V-engine, providing a sufficient volume, avoiding increase in the lateral size of the outboard motor, and reducing the size of the outboard motor with the large-volume engine.
According to another aspect of the present invention, there is provided an outboard motor having a four-stroke engine, which comprises: a generally vertically extending crankshaft; right and left cylinder blocks forming part of a crankcase housing the crankshaft, the cylinder block having a plurality of generally horizontal cylinders vertically adjacent to one another and diverging rearwardly into a V-shape in top plan; cylinder heads connected to rear surfaces of the cylinder blocks to form a plurality of combustion chambers; right and left intake passages provided at inner sides of the cylinder heads in communication with the combustion chambers; a generator disposed forwardly of the crankcase; and an intake silencing box provided above the cylinder blocks in communication with the combustion chambers via the intake passages, wherein the intake silencing box has air induction passages disposed forwardly of exhaust passages located at outer sides of the cylinder heads and extending vertically downwardly between the exhaust passages and a skirt of a crankshaft space in a suspended fashion, the air induction passages having inlets opening downwardly.
The outboard motor thus arranged allows the use of an intake silencer most suitable for a 4-stroke V-engine outboard motor of a large volume and a reduced lateral size, allowing the rational arrangement of an intake system, generator and other components.